Method and apparatus for providing multipoint gaseous fuel injection to an internal combustion engine

ABSTRACT

A multipoint fuel delivery system for an internal combustion engine includes fuel metering device(s) such as fuel injector(s) associated for selectively controlled injection of the second fuel to corresponding combustion chamber(s) of the internal combustion engine. A fuel supply manifold associates with fuel injector(s) for directing the second fuel to each fuel injector. An intake port adaptor mechanism adapts the intake port of the associated combustion chamber to receive the selectively controlled injection of the fuel from an associated fuel injector. The intake port adaptor mechanism may also engage the intake port so as to permit selective flow of the first fuel or the second fuel to the intake port of the selected combustion chamber. A control mechanism selectively controls the flow of the second fuel through each injector(s). The multipoint fuel delivery system make practical both dedicated or single-fuel multipoint injection and, alternatively, selective bi-fuel multipoint injection for an internal combustion engine.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to automotive engine technologyand, more particularly, to a multipoint gaseous fuel injection systemthat provides gaseous fuel to an internal combustion engine byselectively metering the gaseous fuel directly to individual intakeports of the internal combustion engine combustion chambers.

BACKGROUND OF THE INVENTION

Currently, the most accepted method of metering fuel to internalcombustion engines is through the use of pulse-width-modulated (PWM)solenoid valves referred to as fuel injectors. For these engines, amicroprocessor provides control signals of the proper timing andduration for proper fuel delivery by the fuel injectors. Forconventional engines that use liquid fuels, such as gasoline, fuelinjectors are oriented with one end protruding into an intake port nearthe combustion chamber intake valve. The other fuel injector endreceives fuel from a manifolding device. This placement of injectors,one per intake port, is commonly referred to as multipoint injection.

Multipoint fuel injection of alternative fuels is a highly attractivemethod of metering fuel. Multipoint fuel injection, for example, permitsmuch more precise control of fuel flow than do single point orconventional introduction systems. This is particularly important forgaseous fuel engines. Conventional multipoint fuel injection systems,however, do not easily permit either dedicated multipoint alternativefuel injection or bi-fuel multipoint system operation. Most existingalternative fuel systems for gaseous fuels in internal combustionengines introduce fuel upstream of the intake manifold. The intakemanifolds that these engines possess, however, are too large to permitprecise engine control using single point injection upstream of themanifold. With these engines, time lags occur in engine response andlarge fueling errors arise during transient engine operations. Theseengines, for example, often have limited space to accommodate multipointinjection hardware. Also, the costs to convert the existing intakemanifold for multipoint injection may make alternative multipoint fuelinjection impractical. These costs include, for example, tooling,machining, and labor costs for performing complicated installation andmodification procedures for converting a conventional fuel engine toeither a dedicated multipoint engine or a bi-fuel multipoint engine.

Other problems with conventional throttle-body alternative fuel systemsadapted to internal combustion engines relate to the fact that theirintake manifold has a larger volume than does the engine displacementvolume. Because of these large manifolds, throttle-body (single point)gaseous fuel injection systems adapted these engines with large intakemanifolds (1) inaccurately meter fuel; (2) have less than desirabledriveability; and (3) produce higher than desirable emissions.

SUMMARY OF THE INVENTION

Therefore, a need has arisen for a commercially practical fuel systemthat allows dedicated multipoint injection of alternative fuels as wellas bi-fuel engine operation capability on gasoline or conventionalengines. As used herein, dedicated multipoint fuel injection means thatthe only source of fuel to the engine is through a dedicated multipointfuel delivery system. In bi-fuel multipoint fuel injection, an operatormay select to use either a conventional fuel, such as gasoline, or analternative fuel, such as a gaseous fuel.

There is a need for a multipoint injection system for alternative fuelconversions that does not require significant modifications to existinginternal combustion engine hardware.

There is a further need for a multipoint injection fuel system forinternal combustion engines that provides more accurate fuel metering,improved driveability, and the potential for lower emissions whencompared to throttle body or pre-mixed fuel injection systems.

Still, a further need exists for a multipoint gaseous fuel injectionsystem that may be used to provide fuel to virtually any type ofinternal combustion engine. For example, there is the need for amultipoint fuel injection system that may be used with engines withspace constraints or for which intake manifold modifications may be costprohibitive.

In accordance with the present invention, therefore, a method and systemfor multipoint gaseous fuel injection to an internal combustion engineis provided that substantially eliminates or reduces disadvantages andproblems associated with previously developed multipoint fuel injectionsystems. The present invention overcomes or substantially reduces theproblems of engines that introduce fuel upstream of the intake manifoldand permits easy conversion of a multipoint gasoline engine to either adedicated gaseous-fuel engine or a bi-fuel multipointgasoline/gaseous-fuel engine.

More specifically, the present invention provides a method and systemfor multipoint alternative fuel injection to an internal combustionengine. The present invention provides not only dedicated or single fuelmultipoint injection to such an engine, but also a bi-fuel engine thatuses both a conventional fuel such as gasoline and a second oralternative fuel such as a gaseous fuel. For an engine including atleast one combustion chamber, where each combustion chamber includes anassociated intake port, the present invention includes at least one fuelmetering device, such as a fuel injector, such that each fuel injectoris associated for selectively controlled injection of the fuel to theengine combustion chambers. A fuel supply manifold may be, for example,a fuel supply block that holds one or more fuel injectors that are at alocation that is remote from the engine or a fuel supply rail thatsupplies fuel injectors that attach to the engine. The fuel supply blockassociates with the fuel injectors to form a fuel metering valveassembly. The fuel supply manifold associates with each fuel injectorfor directing the fuel from a central location such as a gaseous fuelsupply line to each of the fuel injectors. An intake port adaptermechanism, such as a mixer plate or injector adapter, adapts the intakeport of each combustion chamber to receive the selectively controlledinjection of the fuel from the fuel injectors. The intake port adaptermechanism engages the intake port for permitting flow of the fuel to theintake port of the selected combustion chamber. A control mechanismselectively controls the flow of the fuel through each of the at leastone injector to each of the selected or associated intake ports.

Technical advantages of the invention are that it provides an easy touse and practical method and system that includes the features ofimproved tip-in driveability, more accurate fuel control, reducedexhaust emissions, and reduced start times for gaseous fuel internalcombustion engines.

Another technical advantage of the present invention is that it providesan improved multipoint gaseous fuel injection system that permitslocating fuel injectors in a common location for supplying fuel by acommon fuel supply line and that further plumbs each fuel injector to anassociated intake port and combustion chamber on the engine. The presentinvention provides a practical mechanism for direct and controlledmultipoint fuel injection of an alternative fuel together with theassociated desirable engine performance characteristics of this form offuel injection.

Another technical advantage of the present invention is that it providesa method to convert an internal combustion engine to a multipoint fuelcontrol strategy with minimal modification to the engine. In fact, thepresent invention provides in at least one embodiment a bolt-onmultipoint control system that may be applied to a wide variety ofinternal combustion engines.

Another technical advantage of the present invention is that it providesa method of operation whereby a fuel metering device may be placedremote to the engine with all injectors and sensors in one package orunit and with each injector having an individual tube that routes thefuel to a mixer plate or injector adapter that is mounted to orassociated with the intake port for the engine combustion chambers. Thismakes it practical to use the multipoint control system of the presentinvention with engines having space limitations and cost constraints.

There are other practical embodiments on the invention as described moreparticularly in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptionwhich is to be taken in conjunction with the accompanying drawings inwhich like reference numerals indicate like features and wherein:

FIG. 1 illustrates an internal combustion engine system employing oneembodiment of the present invention;

FIG. 2 illustrates the fuel metering valve assembly and delivery hoseassembly according to one embodiment of the invention;

FIG. 3 shows an isometric view of one embodiment of the fuel meteringvalve assembly of the present invention;

FIGS. 4a and 4b show a mixer plate according to one aspect of thepresent invention and a banjo-type fitting for transfer of the fuel tothe mixer plate, respectively;

FIG. 5 illustrates an alternative embodiment of the invention employinga manifolding device for distributing fuel to alternative fuelinjectors;

FIGS. 6a through 6c illustrate alternative embodiments of the presentinvention in the form of injector adapters for use on the intake port ofa multipoint engine and its associated combustion chamber;

FIG. 7 shows yet a further alternative embodiment of the invention inthe form of an injector nozzle applied to an internal combustion engineintake runner.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the present invention are illustrated in theFIGURES, like numerals being used to refer to like and correspondingparts of the various drawings.

FIG. 1 shows multipoint gaseous fuel delivery system 10 that, in theillustrated embodiment, includes fuel metering valve assembly 12. Fuelmetering valve assembly 12 includes a number of fuel metering valves,such as fuel injectors 14, that inject a fuel into individual cylindersor combustion chambers of engine 16. Output from each fuel injector 14passes through delivery tube 18 to mixer plate 20. Mixer plate 20 ispositioned, for example, in the engine 16 intake manifold betweenmanifold upper section 22 and manifold lower section 24 and provides aseparate path of fuel from each fuel injector to each combustion chamberof engine 16. Engine control module (ECM) 26 receives numerous pressure,temperature and other operating signals from sensors 28 that senseoperating parameters of engine 16. ECM 26 processes these signals and,in response to the processed signals, directs the operation of each fuelinjector 14.

Fuel metering valve assembly 12 receives from pressurized fuel line 30 apressurized fuel from pressure regulator 32. Pressure regulator 32receives gaseous fuel from fuel storage container 34 via high pressurefuel supply line 36.

Engine 16 may be a positive displacement or rotary engine having atleast one cylinder or combustion chamber. Placement of mixer plate 20depends on the many possible embodiments of the present invention. Forexample, mixer plate 20 may be placed between the intake manifold ofengine 16 and the intake ports to each combustion chamber of engine 16.As defined herein, each intake port is that portion of the manifold thatdirects intake air and fuel is separated into one separate path percombustion chamber. Alternatively, mixer plate 20 may be placed in theair/fuel path between the engine head and the intake manifold.Essentially any place that can accommodate the size of mixer plate andthat permits the selective introduction of fuel from fuel injectors 14to the engine 16 combustion chambers is a practical position for mixerplate 20 and clearly within the scope of the present invention.

Although numerous devices may serve the function of ECM 26 to establisha microprocessor-based control system, one system adaptable to thesystem of the present embodiment is Part No. 1707004 that ismanufactured by Mesa Environmental Ventures, Co., of Fort Worth, Tex.ECM 26 may control the operation of fuel injectors 14 according to apredetermined control strategy. The optimal control strategy may varyfor a particular engine and can be determined using test methodologyfamiliar to engine development engineers of ordinary skill in the art.Another controller for controlling the performance of fuel injectors 14may be through the use of the onboard engine controller for a gasolineengine that is modified to control operation of the fuel injectors 14.ECM 26 may also include a harness, sensors and other components toprovide microprocessor-based control of fuel metering valve assembly 12.In FIG. 1, fuel storage container 34 may be a compressed or liquidnatural gas cylinder, an liquid propane gas tank, or other form of fuelstorage tank for gaseous fuels, where the term "gaseous fuel" means afuel that is in a gaseous state under normal ambient conditions.

FIG. 2 illustrates fuel delivery assembly 40 of one embodiment of theinvention. Fuel delivery assembly 40 includes fuel metering valveassembly 12 and fuel delivery hose assembly 42. Fuel delivery hoseassembly 42 protects the individual fuel delivery hoses 18 that go tothe combustion chambers of engine 16. In the embodiment of FIG. 2, fueldelivery hose assembly 42 is bundled using a corrugated loom 44 that isflexible and that protects each individual fuel delivery hose 18. Thisform of fuel bundled assembly 42, however, is optional.

FIG. 3 shows in more detail fuel metering valve assembly 12 thatincludes fuel supply block 46 to which each individual fuel injector 14attaches. Each individual fuel injector 14 includes a connection 48 toECM 26. Cross bars 50 and connecting shafts 52 hold each fuel injector14 securely to fuel supply block 46. Referring now to both FIGS. 2 and3, fuel supply block 46 receives fuel at connection 54 and distributesgaseous fuel to each fuel injector 14. In the preferred embodiment, eachfuel injector 14 is solenoid-operated and outputs to hose connection 56which also attaches to a cross bar 50. Fuel supply block 46 may alsooptionally include temperature sensor 58, pressure sensor 60, and fuelshut-off valve 61.

FIGS. 4a and 4b show views of mixer plate 20 of the present embodiment.Mixer plate 20 is formed to permit its placement between manifold uppersection 22 and the manifold lower portion 24 of each combustion chamberof engine 16 (see FIG. 1). In the embodiment of FIGS. 4a and 4b, mixerplate 20 is configured for a six-cylinder internal combustion engine 16.That is, mixer plate 20 includes six intake openings 62, each having adiameter equivalent to the diameter of the intake port for theassociated combustion chamber of engine 16. Intake opening 62 alsoconnects, via a cross passage, such as cross passage 64, to through-hole66. For secure placement of mixer plate 20 between manifold uppersection 22 and manifold lower portion 24 of engine 16, screwholes 68align to existing screwholes that bolt manifold upper portion 22 tomanifold lower portion 24. Mixer plate 20 has a thickness ofapproximately one-quarter inch, in the embodiment of FIGS. 4a and 4b,and may be made of an aluminum material.

FIG. 4b illustrates a banjo-type fitting 70 that the present embodimentuses in conjunction with mixer plate 20. Banjo-type fitting 70 includesfuel delivery hose connector 72 that receives fuel delivery hose 18 andaround which bevelled washer 74 fits. O-ring 76 fits within bevelledwasher 74 and maintains an airtight seal with the top surface 78 ofmixer plate 20 and connector 72. Along bottom surface 80 of mixer plate20 and opposite banjo-type hose connector 72 is securing mechanism 82.Securing mechanism 82 includes O-ring 84 that maintains an airtight sealbetween bottom surface 80 and delivery hose connector 72. Nut 88 holdshose connector 72 and securing mechanism 82 firmly in place within mixerplate 20.

In operation of banjo-type fitting 70, gaseous fuel flows from fueldelivery hose 18 (FIGS. 1 and 2), through banjo-type fitting 72 and outpassageway 90. When banjo-type fitting 70 is placed within through-hole66, the second or alternative fuel, which is preferably a gaseous fuel,passes into the opening established by the fitting of beveled washers 74and 86 and tightly sealed by O-ring 76 and 84. Fuel then passes intocross-passage opening 92. As FIG. 4 illustrates, from cross-passageopening 92 gaseous fuel passes to outlet 94 and then to associatedintake opening 62 and into the manifold lower portion 24 of engine 16.

The introduction point for the second fuel that the present inventionprovides is at an optimal point relative to manifold dynamics. Each oneof the fuel injectors 14 may respond to a separate sensed signalassociated with its respective combustion chamber and may provide moreor less flow of the second fuel based on that particular combustionchamber's power demand. As opposed to injecting the fuel into the engineintake manifold and then distributing the fuel to all combustionchambers, the present embodiment injects the fuel directly into theintake port of an associated combustion chamber. By selectivelyinjecting fuel into an associated manifold lower portion 24, the presentembodiment more precisely delivers the alternative fuel to the engine.The result is a more responsive engine that is capable of improveddriveability, less hesitation, and better emission control when comparedto other types of engines that introduce fuel upstream of the intakemanifold. In addition, placing the fuel supply at manifold lower portion24 makes it possible for the engine to receive, alternatively, gasolinefuel or a gaseous fuel, such as compressed or liquid natural gas orliquid propane gas fuel. The result is either a monofuel engine with adedicated multipoint fuel injection system or a bi-fuel engine with theselective capability of using two different types of fuel at least oneof which is provided via multipoint injection.

FIG. 5 illustrates an alternative embodiment of the invention thatincludes mixer plate 100 for positioning between manifold upper section22 and manifold lower portion 24. Mixer plate 100 includes fitting 102into which gaseous fuel injector 14 connects. Instead of fitting 102, aboss or other mechanism for introducing fuel into mixer plate 100 may beused. Fuel injector 14 includes connection 48 to ECM 26 (see FIG. 1).Fuel to gaseous fuel injector 14 comes through connection 104 of fuelsupply rail 106. Fuel supply rail 106 receives gaseous fuel directlyfrom pressure regulator 32 and contains pressurized gaseous fuel in fuelsupply passage 108. Pressure sensor 110 may detect and generate a signalindicating the pressure in fuel supply passage 108. Also, temperaturesensor 111 may detect and generate a signal indicating the temperaturein fuel supply passage 108.

FIGS. 6a through 6c illustrate further alternative embodiments of thepresent invention. In particular, FIG. 6a shows injector adapter 120 towhich gasoline fuel injector 122 attaches for delivering the liquidgasoline fuel. Adapter 120 includes input 124 for receiving gas from analternative fuel metering device such as fuel injector 14 of FIG. 1.Adapter 120 substitutes for and eliminates the need for mixer plate 20.FIG. 6b shows an alternative embodiment of the injector adapter 120 ofFIG. 6a as injector adapter 126 that locates gasoline fuel injector 122in its original position relative to the intake manifold. In otherwords, while injector adapter 120 of FIG. 6a slightly elevates gasolinefuel injector 122, injector adapter 126 of FIG. 6b maintains constantthe position of gasoline fuel injector 122 for engines that require sucha design. Injector adapter 126 also includes gaseous fuel input 128.

FIG. 6c shows a further embodiment in the form of injector adapter 130that may receive in combination gasoline fuel injector 122 and naturalgas fuel injector 14, both as previously described. Injector adapter 130further eliminates the need for metering device tube assembly 40 and theassociated metering device tube 18. For injector adapter 130, the secondfuel flows directly from fuel injector 14 to adapter output 132 viagaseous fuel input 134. Fuel supply rail 106 provides gaseous fuel togaseous fuel injector 14. Another embodiment of injector adapter 130that includes the feature of maintaining constant the position ofgasoline fuel injector 122 relative to the intake manifold (similar tothe feature of injector adapter 126 of FIG. 6b) is also within the scopeof the present invention.

FIG. 7 illustrates a further alternative embodiment 140 of themultipoint gaseous fuel delivery system of the present invention. Inparticular, from fuel metering valve assembly 12, fuel delivery tube 18connects to injector nozzle 142. Injector nozzle 142 fits within aformed hole or penetration 144 of intake manifold 146. From injectornozzle 142 the fuel enters intake manifold 146 through passage 143 andpasses directly into engine 16. This embodiment may be desirable toovercome space limitations near engine 16 and where it is practical toremotely use fuel metering valve assembly 12.

OPERATION

In operation and with reference to FIGS. 1 through 4, multipoint fueldelivery system 10 provides an alternative or second fuel to internalcombustion engine 16 for improved control in both steady state andtransient operations. To more fully understand the operation ofalternative fuel delivery system 10, consider the instance of steadystate engine operation. Engine pressure and temperature signals, as wellas other engine control signal inputs, go to ECM 26 for the generationof control signals to each of fuel injectors 14 on fuel metering valveassembly 12. Based on control signals from ECM 26, one or more of fuelinjectors 14 will open to send fuel from line 30 through a respectivefuel delivery tube 18.

As fuel enters tube 18, it passes to mixer plate 20 where, usingbanjo-type fitting 70, fuel passes into through-hole 66 and into crosspassage 64. From cross passage 64, fuel passes to intake opening 62.From intake opening 62, the alternative fuel goes directly into therespective manifold lower portion 24 and into the engine combustionchamber. This provides the necessary fuel to respond to the engine 16demand for the respective combustion chamber. This combustion chamberoutput directly affects the pressure temperature and other sensedparameters that go to engine control module 26. In response, enginecontrol module 26 will send adjusted signals to each of fuel injectors14 on fuel metering valve assembly 12. The other embodiments describedin FIGS. 5 through 7 operate in an essentially similar manner. Theresult, irrespective of the embodiment, is a more responsive internalcombustion engine with multipoint injection capability.

The direct benefits of the present embodiment include improveddriveability, improved tip-in response, and reduced emissions relativeto throttle body and other forms of alternative fuel injection. This isdue to the more immediate and direct control that the present embodimentprovides.

Although the invention has been described with reference to theabove-specified embodiments, this description is not meant to beconstrued in a limiting sense, various modifications of a disclosedembodiment, as well as alternative embodiments of the invention willbecome apparent to persons skilled in the art upon reference to theabove description. It is therefore, contemplated that the appendedclaims will cover such modifications that fall within the true scope ofthe invention.

What is claimed is:
 1. A multipoint bi-fuel engine capable of using afirst fuel and a second fuel, comprising:an engine capable of using thefirst fuel and comprising at least one combustion chamber, eachcombustion chamber having an intake port; at least one fuel meteringdevice for selectively controlled injection of the second fuel to acorresponding one of the at least one combustion chamber; a fuel supplymanifold associated with said at least one fuel metering device fordirecting the second fuel to each of said at least one fuel meteringdevice; an intake port adapter mechanism for adapting the intake port ofa selected one of said at least one combustion chamber to receive theselectively controlled injection of the second fuel from a selected oneof said at least one fuel metering device, said intake port adaptermechanism engaging the intake port for selectively flowing the secondfuel to the intake port of the selected combustion chamber; at least onefuel supply hose each said hose having a first end coupled to one ofsaid at least one fuel metering device and having a second end coupledto said intake port adapter mechanism; and a control mechanism forselectively controlling the flow of the second fuel through each of saidat least one fuel metering device.
 2. The multipoint bi-fuel engine ofclaim 1, further comprising a fuel metering valve assembly having a fuelsupply block associating with each of said at least one fuel meteringdevice, said fuel metering valve assembly for receiving the second fueland distributing the second fuel to said selectively controlled at leastone fuel metering device.
 3. The multipoint bi-fuel engine of claim 1,wherein said intake port adapter mechanism comprises mixer plate, saidmixer plate comprising at least one fuel receiving mechanism and atleast one intake port opening, each of said at least one fuel receivingmechanism and said intake port opening associated with a selected one ofsaid at least one combustion chamber and comprising a cross-passageconnecting to a selected one of said at least one intake port opening.4. The multipoint alternative bi-fuel engine of claim 1, wherein saidintake port adapter mechanism comprises a mixer plate, said mixer platecomprising at least one fuel receiving mechanism and at least one intakeport opening, each of said at least one fuel receiving mechanism andsaid intake port opening associated with a selected one of said at leastone combustion chambers and comprising a cross-passage connecting to aselected one of said at least one intake port opening, and furtherwherein each of said at least one fuel receiving mechanism receives anddirects the second fuel from said selected injector to a selected intakeport.
 5. A multipoint fuel injection method for introducing analternative fuel into an internal combustion engine designed to operatewith a conventional fuel, the engine having a plurality of combustionchambers, each combustion chamber having an intake port, the methodcomprising the steps of:selectively controlling the injection of thealternative fuel from at least one injector associated with acorresponding one of at least one associated intake port; directing thealternative fuel to each of said at least one injector using a fuelsupply manifold associated with said at least one injector; receivingthe selectively controlled injection of the alternative fuel from aselected one of said at least one injectors using a fuel supply hosehaving a first end coupled to the injector and a second end coupled toan intake port adapter mechanism that adapts the intake port of aselected one of said at least one combustion chamber by engaging theintake port with said intake port adapter mechanism so as to permitselective flow of the alternative fuel to the intake port of theselected combustion chamber; and selectively controlling the flow of thealternative fuel through each of said at least one injectors using acontrol mechanism.
 6. The method of claim 5, further comprising the stepof distributing the alternative fuel to the selectively controlled atleast one fuel injector using a fuel supply block.
 7. An intake portadapter system for providing multipoint fuel delivery to an internalcombustion engine the engine being a conventional engine having a fuelsystem that operates with a conventional fuel, the engine having aplurality of combustion chambers, each combustion chamber having anintake port, each intake port having a diameter, the system comprising:amixer plate associated with each intake port, each mixer plate providingan alternative fuel to each intake port, each mixer plate having agenerally flat configuration adapted for placement along each intakeport, and each mixer plate having an intake opening, the intake openinghaving a diameter corresponding to the diameter of the intake port; anda fuel receiving fitting associated with each mixer plate for providingfuel to each intake opening.
 8. The system according to claim 7 furthercomprising a fuel metering device associated with each fuel receivingfitting, the fuel metering device for selectively introducing fuel tothe corresponding intake opening.
 9. The system according claim 8further comprising a fuel delivery hose having a first end connected tothe fuel metering device and having a second end connected to the fuelreceiving fitting.
 10. The system according to claim 7 furthercomprising:a fuel metering valve assembly adapted to hold each fuelmetering device, the valve assembly having a fuel connection foraccepting alternative fuel from an alternative fuel supply and having afuel supply block for supplying alternative fuel to each fuel meteringdevice; and a control mechanism associated with the fuel metering valveassembly for selectively controlling the flow of fuel through each fuelmetering device.
 11. The system of claim 7, wherein the alternative fuelis a compressed natural gas fuel.
 12. The system of claim 7, wherein thealternative fuel is liquid propane gas fuel.
 13. The system of claim 10,further comprising a temperature sensor associated with the internalcombustion engine, and wherein said control mechanism responds to sensedtemperature of the internal combustion engine.
 14. The system of claim10, further comprising a pressure sensor associated with the infernalcombustion engine, and wherein said control mechanism responds to sensedpressure of the internal combustion engine.